The present invention relates to cooling systems. More particularly, the invention relates to cooling systems for cooling a person in a supine position.
There are circumstances in which it may be desirable to positively cool a patient as part of clinical treatment. For example, recent investigations have indicated that benefits may arise by subjecting patients who have suffered a stroke or cardiac arrest to mild hypothermia, e.g. a temperature in the range of 32 to 34xc2x0 C. for a period of more than about 1 hour after the cardiac arrest. This clinical procedure is described in the paper by Fritz Sterz et al. in the Journal of Neurological Anaestheology, Volume 8, No. 1, pages 88 to 96, published 1996.
It is, therefore, an object of the present invention to provide a method and equipment for carrying out such a clinical procedure, as well as for cooling patients for other purposes.
According to one aspect of the present invention, therefore, there is provided a method of cooling a person in a supine position on a support which comprises passing cooled air through a flexible jacket which underlies or overlays the person, said jacket preferably having apertures to allow escape of cooling air. Preferably, the jacket is adapted to overlay the person and to cover at least his torso. In an especially preferred form, the jacket or blanket substantially covers the person from head to foot.
The present invention includes a mattress which is associated with a heat exchanger, the heat exchanger being connectable to a source of cooling fluid such as water so that the patient may be cooled as required, by connecting the heat exchanger to a source of cooled liquid, such as refrigerant.
According to a further feature of the present invention, therefore, there is provided a mattress having inflatable compartments for supporting a person thereon, and an air supply means for supplying pressurized air to the mattress, said mattress having a heat exchanger associated therewith, through which said pressurized air can be passed and said heat exchanger being connectable as required to a source of cooling fluid, such as a refrigeration circuit, whereby pressurized air can be cooled as required, and applied directly to the patient or to a jacket or blanket in contact with the patient.
Preferably, in such a mattress, the source of air comprises a pump unit having an outlet for connection to the inflatable compartments, and an outlet for connection to an inflatable cooling jacket or blanket.
The heat exchanger may be located in a housing physically attached to the mattress or to a bed on which the mattress is supported. Alternatively, the heat exchanger may be contained in a separate unit and connected to the mattress (and/or cooling jacket or blanket) by conduits, which are normally flexible.
The heat exchanger is conveniently supplied with cooling liquid, either by being incorporated in a refrigeration circuit in which the heat exchanger is on the expansion side, or fed with cooling fluid from a refrigeration system. In the latter case, the cooling fluid s generally water or an aqueous liquid such as brine, and is cooled by contact with the heat exchanger of a refrigeration circuit. This arrangement has the advantage that the cooling fluid circuit, such as water, provides a heat reservoir which irons out sharp fluctuations in temperature in the system. However, the former, more direct, cooling system works satisfactorily and has a quicker start up and will attain steady state more quickly. Preferably, a regulator valve is introduced into the refrigeration circuit and controls the flow of refrigerant as required to maintain a desired temperature at the supporting surface of the mattress. This can be achieved, for example, by using a solenoid regulator hot gas by-pass valve in the refrigeration circuit, which is controlled by a digital PID controller connected to one or more temperature sensors at the exit end of the heat exchanger.
It is convenient to extract heat from an air stream by blowing air over the heat exchanger and feeding the pressurized, cold air to the mattress and also to the cooling jacket or blanket. Normally, the air supplied to the mattress is intended to be sufficient to provide support for the patient as well as to provide the desired cooling effect. Where the same blower is used to supply air both to the mattress and jacket/blanket, the majority of the air will be directed to the mattress.
Some of the air supplied to the mattress will pass to atmosphere via exhaust valves in the mattress for controlling air pressures in the inflated compartments of sacs of the mattress. Other quantities of air will escape via stitch holes in the surface of the mattress and form air streams which cool the patient by passing over his skin. Heat will also be abstracted from the patient by conduction through the surface of the mattress and by cooling air emitted from apertures in the cooling jacket or blanket.
It may be necessary to provide means to confine the patient to prevent shivering.
In the operation of the patient cooling system of the invention, the objective is to effect moderate to mild hypothermia, i.e. a body temperature of about 32 to 34xc2x0 C. It is found that this can be achieved with the mattress and jacket/blanket of this invention using an air input temperature to the apparatus of about 1 to 3xc2x0 C., preferably about 2xc2x0 C. The mattress surface temperature should be less than 10xc2x0 C., preferably about 5 to 10xc2x0 C. Studies have indicated that clinical benefits are obtained in terms of reduction in brain damage if the temperature of the patient who has suffered cardiac arrest is reduced to a temperature in the range of 32 to 34xc2x0 C. within a few hours, preferably within 2 to 4 hours, of restoration of spontaneous circulation (ROSC). Hypothermia treatment needs to be started quickly after ROSC, e.g. within about 15 minutes.
Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings, exemplary detailed description and appended claims.